It looks like Star Wars: Battlefront II is going to help fill in some information regarding Luke Skywalker and what led him on his journey to the Jedi Temple on Ahch-To. It's a pretty cool detail that offers fans a little insight.
According to GamesRadar, one of the missions in the campaign leads an Inferno Squad member named Del Meeko to a planet called Pillio. His mission on the planet is to destroy everything in the Emperor’s vault.
On his journey he runs into Luke Skywalker, who has been guided by The Force to the Emperor's vault. The two reluctantly team up and end up finding the vault. It's there that Luke sees a star map. This is the same star map with the compass that we saw in the trailer for Star Wars: The Last Jedi.
It seems like this is the place where Luke begins his journey that will eventually lead him to the Jedi temple on Ahch-To. The report goes on to say:
That compass leads him to something very important on Ahch-To. There’s a Jedi Temple on the island – it seems the Emperor knew about it – but what’s inside could be one of the biggest secrets in Star Wars history.
Unfortunately, we're all just going to have to wait to see what that secret turns out to be. We know that there is some Jedi scripture at the temple, but what has Luke learned in reading it? Hopefully, some of these questions will eventually be answered over the course of the two upcoming films in the Star Wars saga.